I would definitely suggest switching to a larger tank. In my opinion, glass is just... better.
As you said, it also makes it easier to use the heater. Not only this, but you can install a good filter so that you don't have to do such frequent water changes and your frogs have a lot more room to play! Again just my opinion. Most suggest having at least 2.5 gallons per frog.

I've used tinted dechlorinators before but they never tinted the water, I haven't heard of the brand you're using.